diff --git a/AGENTS.md b/AGENTS.md
index bfe0976fd..6682f71a4 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -305,6 +305,12 @@
 
 - Follow existing node conventions: `INPUT_TYPES`, `RETURN_TYPES`, `FUNCTION`,
   `CATEGORY`, and registration through the local mapping used by that file.
+- Treat legacy combo inputs, `io.Combo`, and `io.DynamicCombo` values as
+  untrusted when they affect filesystem access. Any value used as a file or
+  folder name, path component, format, or extension must be validated again at
+  the load/save boundary using an existing `folder_paths` resolver or
+  containment helper, or a fixed allowlist/mapping. Do not rely only on the
+  advertised combo options or prompt validation.
 - Keep node changes backward compatible by default. Add inputs with sensible
   defaults and avoid changing output types unless the request requires it.
 - Model implementations should add the minimal number of ComfyUI nodes required
diff --git a/comfy_api/latest/_ui.py b/comfy_api/latest/_ui.py
index b48713d41..f1f359e6a 100644
--- a/comfy_api/latest/_ui.py
+++ b/comfy_api/latest/_ui.py
@@ -260,6 +260,7 @@ class ImageSaveHelper:
 class AudioSaveHelper:
     """A helper class with static methods to handle audio saving and metadata."""
     _OPUS_RATES = [8000, 12000, 16000, 24000, 48000]
+    _FORMATS = {"flac", "mp3", "opus"}
 
     @staticmethod
     def save_audio(
@@ -270,6 +271,9 @@ class AudioSaveHelper:
         format: str = "flac",
         quality: str = "128k",
     ) -> list[SavedResult]:
+        if format not in AudioSaveHelper._FORMATS:
+            raise ValueError(f"Unsupported audio format: {format!r}")
+
         full_output_folder, filename, counter, subfolder, _ = folder_paths.get_save_image_path(
             filename_prefix, _get_directory_by_folder_type(folder_type)
         )
diff --git a/comfy_extras/nodes_dataset.py b/comfy_extras/nodes_dataset.py
index 5e0454d8b..71e5ee368 100644
--- a/comfy_extras/nodes_dataset.py
+++ b/comfy_extras/nodes_dataset.py
@@ -195,7 +195,7 @@ class LoadImageDataSetFromFolderNode(io.ComfyNode):
 
     @classmethod
     def execute(cls, folder):
-        sub_input_dir = os.path.join(folder_paths.get_input_directory(), folder)
+        sub_input_dir = secure_subfolder_path(folder_paths.get_input_directory(), folder)
         valid_extensions = [".png", ".jpg", ".jpeg", ".webp"]
         image_files = [
             f
@@ -241,7 +241,7 @@ class LoadImageTextDataSetFromFolderNode(io.ComfyNode):
     def execute(cls, folder):
         logging.info(f"Loading images from folder: {folder}")
 
-        sub_input_dir = os.path.join(folder_paths.get_input_directory(), folder)
+        sub_input_dir = secure_subfolder_path(folder_paths.get_input_directory(), folder)
         valid_extensions = [".png", ".jpg", ".jpeg", ".webp"]
 
         image_files = []
@@ -310,7 +310,7 @@ class LoadVideoDataSetFromFolderNode(io.ComfyNode):
 
     @classmethod
     def execute(cls, folder):
-        sub_input_dir = os.path.join(folder_paths.get_input_directory(), folder)
+        sub_input_dir = secure_subfolder_path(folder_paths.get_input_directory(), folder)
         video_files = sorted([
             f for f in os.listdir(sub_input_dir)
             if any(f.lower().endswith(ext) for ext in VALID_VIDEO_EXTENSIONS)
@@ -357,7 +357,7 @@ class LoadVideoTextDataSetFromFolderNode(io.ComfyNode):
 
     @classmethod
     def execute(cls, folder):
-        sub_input_dir = os.path.join(folder_paths.get_input_directory(), folder)
+        sub_input_dir = secure_subfolder_path(folder_paths.get_input_directory(), folder)
 
         video_files = []
         for item in sorted(os.listdir(sub_input_dir)):
diff --git a/comfy_extras/nodes_gaussian_splat.py b/comfy_extras/nodes_gaussian_splat.py
index 116c14fde..a53317b4e 100644
--- a/comfy_extras/nodes_gaussian_splat.py
+++ b/comfy_extras/nodes_gaussian_splat.py
@@ -471,6 +471,12 @@ def _mat_to_quat(m):
 
 
 class SplatToFile3D(IO.ComfyNode):
+    FORMAT_WRITERS = {
+        "ply": _gaussian_ply_bytes,
+        "ksplat": _gaussian_ksplat_bytes,
+        "spz": _gaussian_spz_bytes,
+    }
+
     @classmethod
     def define_schema(cls):
         return IO.Schema(
@@ -482,7 +488,7 @@ class SplatToFile3D(IO.ComfyNode):
                         "Supports one item per batch only.",
             inputs=[
                 IO.Splat.Input("splat"),
-                IO.Combo.Input("format", options=["ply", "ksplat", "spz"],  # TODO: add "splat" when we have a writer for it
+                IO.Combo.Input("format", options=list(cls.FORMAT_WRITERS),  # TODO: add "splat" when we have a writer for it
                                tooltip="ply: standard 3D Gaussian Splat with full spherical harmonics. "
                                        "ksplat: mkkellogg SplatBuffer (level 0, uncompressed), base color only "
                                        "spz: Niantic gzip-compressed (~10x smaller), base color only "
@@ -493,10 +499,13 @@ class SplatToFile3D(IO.ComfyNode):
 
     @classmethod
     def execute(cls, splat, format="ply") -> IO.NodeOutput:
+        writer = cls.FORMAT_WRITERS.get(format)
+        if writer is None:
+            raise ValueError(f"Unsupported splat format: {format!r}")
+
         if splat.positions.shape[0] > 1:
             logging.warning("SplatToFile3D supports one item per batch only. Got %d; using first.", splat.positions.shape[0])
         end = _real_len(splat, 0)
-        writer = {"ksplat": _gaussian_ksplat_bytes, "spz": _gaussian_spz_bytes}.get(format, _gaussian_ply_bytes)
         data = writer(splat.positions[0, :end], splat.scales[0, :end],
                       splat.rotations[0, :end], splat.opacities[0, :end], splat.sh[0, :end])
         return IO.NodeOutput(Types.File3D(BytesIO(data), file_format=format))
diff --git a/nodes.py b/nodes.py
index de86e93fe..08529d8dc 100644
--- a/nodes.py
+++ b/nodes.py
@@ -633,15 +633,18 @@ class DiffusersLoader:
     SEARCH_ALIASES = ["load diffusers model"]
 
     @classmethod
-    def INPUT_TYPES(cls):
+    def _model_paths(cls):
         paths = []
         for search_path in folder_paths.get_folder_paths("diffusers"):
             if os.path.exists(search_path):
                 for root, subdir, files in os.walk(search_path, followlinks=True):
                     if "model_index.json" in files:
                         paths.append(os.path.relpath(root, start=search_path))
+        return paths
 
-        return {"required": {"model_path": (paths,), }}
+    @classmethod
+    def INPUT_TYPES(cls):
+        return {"required": {"model_path": (cls._model_paths(),), }}
     RETURN_TYPES = ("MODEL", "CLIP", "VAE")
     FUNCTION = "load_checkpoint"
     DEPRECATED = True
@@ -649,14 +652,20 @@ class DiffusersLoader:
     CATEGORY = "model/loaders"
 
     def load_checkpoint(self, model_path, output_vae=True, output_clip=True):
+        if model_path not in self._model_paths():
+            raise ValueError(f"Invalid diffusers model path: {model_path!r}")
+
+        resolved_model_path = None
         for search_path in folder_paths.get_folder_paths("diffusers"):
             if os.path.exists(search_path):
                 path = os.path.join(search_path, model_path)
-                if os.path.exists(path):
-                    model_path = path
+                if os.path.isfile(os.path.join(path, "model_index.json")):
+                    resolved_model_path = path
                     break
+        if resolved_model_path is None:
+            raise FileNotFoundError(f"Diffusers model {model_path!r} not found.")
 
-        return comfy.diffusers_load.load_diffusers(model_path, output_vae=output_vae, output_clip=output_clip, embedding_directory=folder_paths.get_folder_paths("embeddings"))
+        return comfy.diffusers_load.load_diffusers(resolved_model_path, output_vae=output_vae, output_clip=output_clip, embedding_directory=folder_paths.get_folder_paths("embeddings"))
 
 
 class unCLIPCheckpointLoader: